The present invention relates to an improved apparatus for forming a longitudinally corrugated thin strip into a flexible corrugated tube generally like that disclosed in U.S. Pat. No. 4,141,385, issued Feb. 27, 1979.
The prior art apparatus known to applicant which is pertinent to the present apparatus includes that of U.S. Pat. No. 4,058,997, issued Nov. 22, 1977; U.S. Pat. No. 4,353,232, issued Oct. 12, 1982 on an application filed Jan. 28, 1980; and United Kingdom application No. 2027373A, published Feb. 20, 1980.
Apparatus of the type disclosed in U.S. Pat. No. 4,058,997 may be used to produce tubes of different diameters only by removing from the apparatus a plate which carries a circle of forming rollers which are tangent to a circle of one diameter, and replacing that plate with another one which carries rollers that are tangent to a circle of a different diameter. As a result, switching the machine from the manufacture of a tube of one diameter to that of another diameter is quite a complex and time consuming job.
U.S. Pat. No. 4,353,232 has an adjusting arrangement to make ducts of different sizes, but adjustment is relatively slow because each of the curling guide rollers must be individually removed from one mounting hole and firmly secured in another mounting hole at a different radial position; and in addition the required change in the helix angle for ducts of different diameters must also be separately set.
The apparatus of published U.K. application No. 2027373A has a mechanism for simultaneously moving all the curling guide rollers from one radial position to another; but the mechanism is cumbersome because the adjustments function from the outer periphery of the curling head, which requires a succession of connected drive shafts around a circumference which must be substantially larger than that of the largest duct to be formed.
A large percentage of the flexible corrugated tubes made in this type of machine are used for air conditioning ducts, and any particular air conditioning installation usually requires ducts in several different sizes. A portable duct curling machine may be used to produce duct as needed at a job site, and there are portable units for this purpose. In another system a duct curling machine is located so as to serve heating and air conditioning contractors in a relatively small area to custom produce their needs for specific jobs. This has the advantage of offering better quality control than is usual with "on site" fabrication.
Portable apparatus of a type heretofore developed by the present inventor in Germany utilizes a cassette to receive a reel of precorrugated strip which is used in the fabrication of the flexible corrugated tube.